This project analyzes the mechanisms and physiologic significance of eukaryotic DNA transmethylation using homogeneous purified DNA methyltransferases and homo-non-methylated DNA substrates isolated from the same cell types. The physicochemical properties of DNA methylase from Novikoff rat hepatoma cells will be analyzed with respect to molecular weights, substrate requirements, reaction kinetics, and the exact nucleotide sequences extant in and near methylatable sites. Enzyme cofactor analogues will be tested as inhibitors of DNA methylase in vitro with subsequent in vivo tests to determine the specificity of inhibition. The homologous DNA methylase - homo-non-methylated duplex DNA system will be utilized to probe for mammalian restriction endonucleases. DNA methylation will also be analyzed in the Xenopus laevis oocyte-developing embryo system.